1. Field of the Invention
The present invention relates to a battery-powered vacuum cleaner powered by a battery, such as a lithium ion secondary battery or a nickel metal hydride secondary battery, and a method of cooling the battery-powered vacuum cleaner. More particularly, the present invention relates to a heat radiating structure for a battery pack, and a method of cooling the battery pack.
2. Description of the Related Art
FIG. 13A and FIG. 13B are schematic sectional views of a conventional vacuum cleaner. A battery pack container 2 formed in a casing (housing) 1 of the vacuum cleaner. The battery pack container 2 is formed of a concave wall continuous with the casing 1, and a removable cover fastened with a screw to facilitate changing a battery pack 3. The battery pack 3 contained in the battery pack container 2 is formed by bundling a plurality of secondary batteries in a heat-shrinkable tube. The battery pack 3 supplies power to a motor 7 having an output shaft holding a fan 5, and a control circuit for controlling the motor 7. The battery pack 3 generates heat due to the internal resistances of the batteries 4 and the resistances of the wires connecting the batteries 4 when the vacuum cleaner operates. To drive the motor 7, the battery pack 3 needs to supply a high current and generates heat energy at a high rate. Excessive temperature rise in the batteries 4 must be avoided to operate the batteries 4 at high charge-discharge efficiency, i.e., to discharge the largest possible amount of energy stored in the batteries 4. Therefore the battery pack 3 generating heat must be cooled. A side wall, on the side of a dust cup 9, of the battery pack container 2 is provided with slits 10 to facilitate cooling the battery pack 3. Air used for sucking dust is guided to the motor 7 to cool the motor 7, and then the air passed the motor 7 is guided so as to flow through the vicinity of the battery pack container 2. The battery pack 3 is formed by bundling the cylindrical secondary batteries 4 in the heat-=shrinkable tube, and wiring lines are extended fro the battery pack 3. The air containing dust and sucked through a hose 14 by the fan 5 is guided into the dust cup 9, the air flows through a filter 17 outside the dust cup 9, and the thus filtered air is guided to the vicinity of the motor 7 to air-cool the coils and the components of the motor 7. The air used for air-cooling the motor 7 is discharged outside through a discharge openings 12 formed in an end all of the housing 1. Wheels 19 and 20 are attached to the bottom wall of the casing 1.
In this conventional vacuum cleaner, the air sucked by the fan 5 and cooled the motor 7 is guided to the battery pack container 2 to cool the battery pack 3. The battery pack 3 cannot be efficiently cooled because the air heated by heat generated by the motor 7 is used for cooling the battery pack 3.